Sound recording and reproducing apparatus



June 24, 1930. R. H. TOWNSEND SOUND RECORDING AND REPROD UCING APPARATUS Filed Jan. 13, 1925 Q \A 1 mvgmoa ATTORNEYS,

Patented June 24, 1930 UNITED STATES PATENT OFFICE RALPH H. TOWNSEND, OF MOUNT VERNON, NEW YORK, ASSIG-NOR TOwTHE BRUNSWICK- IBALKE-COLLENDER COMPANY, 01! WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE SOUND RECORDING AND REPRODUCING APPARATUS Application filed. January 13, 1925. Serial No. 2,064.

l This invention relates to apparatus for respond with the sound variations.

cording and reproducing sounds electrically and is directed to the rovision of electric recording and reproducmg apparatus of an improved construction whereby more faithful reproduction of recorded sounds may be obtained.

The invention may be employed in a re .corder actuated by the fluctuations of electric current flowin in a circuit to oscillate a suit able stylus am? thereby cut or otherwise form a record groove whose undulations corre- Or, the invention may be embodied in a reproducer in which an oscillating member is oscillated by the undulations of a record groove and generates a fluctuating current in an electric cir-' cuit. This circuit may. be extended to a sound reproducer located at a desired point and if the fluctuating current is of insuflicient strength to develop the required volume of sound it may be amplified by including in the circuit a suitable audio-frequency cascade amplifier using resistance coupling between successive stages. j

The improved sound recording and reproducing apparatus includes a magnet, which may be either a permanent magnet or an electro-magnet, and may have either a solid or a laminated core, and a pivotally mounted member cooperating'therewith as an armature. Assoclated with these parts is a coil included in a circuit in which a fluctuating .current flows, this current being employed to eifect the .oscillation of the armature 1n the case of a recorder or being developed in the' circuit by the oscillation of the armature when the latter is actuated b a sound record. Sound recording and repro ucing ap aratus of this general character has been ma e heretofore' and it is the object of this invention to provide an improved construction for such apparatus whereby superior results are ob-' tained, all to the end that 'more faithful remeans of this without sacrificing rigidit to too reat an extent. It should be rigi to a big degree so .that oscillations imparted to it will not be absorbed in it to any appreciable extent and by making it of very-light weight it will respond more promptly and more accurately to the forces applied to it tending to oscillate it. His pivoted at apoint close to its center of inertia for in that way also greater accuracy of response in movement of the armature to the forces applied to it is obtained. 7

' Parts on this armature are disposed between or adjacent to the poles of the magnet but the widthof the air gap between these parts and the poles is made large relatively to the range of oscillation of the parts of the armature so that these parts are at all times spacedfrom the poles of the magnet by a considerable distance. When the armature is in its normal or mid-position, it is acted upon equally by the two poles, but when it .is moved to carry one part closer to a pole,

that pole immediately becomes more efiective to attract the armature still closer to it. By making the width of the air gap large compared to the range of movement of the parts of the armature, the effect of this increasing attractive power of the pole as the part of the armature moves toward it is minimized and this may be to such extent that it is practicably negligible.

In reproducing and recording apparatus of this type, it is necessary to provide a suitable means for damping the movements of the armature by holding it yieldingly in its mid position and tending to return it to that positlon when it has been moved from it. One of the features of the present invention involves the provision of an im roved form of damping means. The use 0 a spring or elastic diaphragm has heretofore been proposed for this urpose but with a damping orm'the results obtained are much less perfect than is desired. If the spring or diaphragm is made relatively stifi' it imposes too much resistance to the desired oscillatory movements of the armature, and on the other hand if it is made less stifi' so that its resistance .is not too -great, its own resonance characteristics are impressed upon sults obtained.

l-hav'e procured far superior results bythe use of .a damping means in the form of a sponge rubber pacln'ng bearing upon the armature and compressed more or less by the oscillatory movements thereof. Such a. non-metallic, non-resonant packing holds thefarmature yieldingly in its mid position. and serves adequately 'to return it to that position when it has been moved and there is an entire absence of the super-position upon the armature of'a foreign resonance characteristic.'.Also, with such a damping means provision for regulation can be made quitereadily asfor instance by the use of a screw or similar means for compressing the rubber packing more or less 'as may be-required. i

- The invention may be embodied in a form employing a magnet having its poles facing each other, and an armature in the found a straight bar of considerable rigidity pivoted at about its center and with one end lyin between the two pole faces. This end of t connected in an electric circuit s'o-that the coil-receives the fluctuating electric current which effects the oscillation of the armature or has such a current developed in it by the oscillation of the armature. The width of the gap between the pole faces is made large with relation to the range of oscillation of the armature and the soft rubber which constitutesthe damping means is mounted in and bearing upon opthe a of themagnet g p Or if desired,

'posite sides of the armature.

the poles of the magnet may face in the same direction and the light, rigid, pivoted armature may be bifurcated on one side of its pivot to provide arms extending in proximity to the poles; also, if desired the coil may encircle some portion of the magnet instead of the armature. Whatever the construction may be in these respects, the con struction characteristic of the invention involves'the use of a light rigid armature V pivoted at a point adjacent to its center of inertia and having parts adjacent to the poles of the magnet, therange of oscillation of the armature being small compared to the gap between the pole faces and the adjacent faces of' the armature, together with damping means for holding the armature yieldingly in its central position, this damping means being prefera ly .in the form of the soft rubber packing above referred to.

I have-illustrated in the drawings annexed hereto embodiments of the invention with which good results may be obtained. In these drawings, Fig. 1 is a face view of a sound recorder embodying the invention,

partly in section on line 1-1- of Fig. 2; Fig.

2 is a side view of the construction shown in Fig. 1; Fig. 3 is a view of the recorder e bar may also'extend through a coil that the parts the pole faces are-always held at a sub- Referrin first to Figs. 1 to 4, a permanent magnet is s own at 7 of the usual horse shoe -form having its poles turned toward each other and an air gap of substantial size'between the poles faces. This magnet is secured by a strap 8 and screw 9 to a frame piece 10 on which is formed a socket 11 to receive the end of the supporting arm by which the, recorder is moved across the face of a disc sound record-while cutting a record piece 10 is turned laterally at 12 to form a bra'cketto which is secured a support 13. The armature is pivotally mounted upon this support.- In the present instance of a sound recorder, this armature 14 is a cutter bar adapted to have a suitable cutting jewel secured to its lower end. In the case of a reproducer the armature would be a stylus bar having secured to its lower end a stylus adapted to track in the groove of a sound record. In either case the armature would be a light rigid bar, made as light as possible without sacrificin rigidity to too great an extent, and pivotafiy mounted at about its center of inertia. In the present instance the armature is shown as inte ral with a horizontal member 15, both en s of which are pointed and fit in bearings. 'Oneof these bearings is formed in a stud 16 on the support 13 and the other is made adjustable by being formed in the end of a stud 17 threadedin a bracket 18 on the support 13. With this form of mounting vibrational movement of the armature relative to its bearings which would give rise to what is known as chattering is prevented.

' The upper'end of the armature extends ulp into the space between the pole faces of t e magnet 7 and surrounding this portion of the armature is a coil 23 which is mounted upon therbracket 12. The ends of this coil are electrically connected to terminals 24 mounted on a block 25 of insulating material secured to the frame 10. The dampof the magnet 7 and the adjacent side of the upper end of the armature 14 and both of groove therein. At its lower edge the frame them resting upon the top surface of the spool on which the'coil 23 is wound.

The construction of the invention thus described is distinctive in the respects that the armature is a rigid light member pivotally mounted at about. its center of in ertia and having parts which lie adjacent to the pole faces of the magnet, the oscillations of this armature being suitablydamped and occurring within such a range of the armature adjacent to I stantial distance from those faces by reason of the width of the gap between the pole faces and the adj acent faces of the armature relative to the amplitude of oscillation of the armature. By reason of the use of this arrangement, the damping eifect may be very light with the result that there will a be proportional response of the movement of the armature to forces applied to it throughout the whole of its range of movement, and, in the case of a reproducer, less wear upon the, record. It is well to use high silicon steel in making the armature to the end that rigidity and light weight may be combined to a high degree. For the same reason the armaturemay be of tubular con- -struction or may be made of I-beam conthem to more or less pressure in any suitable manner.

When a fluctuating current is impressed upon the coil 23 of the recorder, the magnetic field developed by the coil reacts upon the field of force of the magnet 7 within which the end of the armature 14 lies and the armature is oscillated on its pivot in exact accordance with these fluctuations, following them the more accurately because of its light weight and rigidity, the 1 arrangement of the pivot, the relation of the amplitude of its movement to the width of the air-'.

The damping means 'is of the ture on said pivot bar including a portion dis osed in said air gap, a coil carried by sai portion of the frame piece and disposed about said armature, and means in said air gap for dampening movement of said armature.

In testimony whereof I afiix my signature. y

RALPH H. TOWNSEND.

gap of the magnet, and the damping effect of the non-metallic non-resonant blocks. In the case of a reproducer, the armature is oscillated by the tracking of the stylus carried by it in the record groove and the moveot er, said ments of its upper end develops a-fluctuating current in the circuit of coil 23, the strength of this current being dependent upon the number of turns in coil .23, the strength of the field of magnet 7 and the rate of change of position of the armature with respect to the coil and the pole tips. The fluctuating current so produced may be led to ear-phones or similar apparatus and if it is not of sufficient strength it may be carried through an audio frequency amplifier.

I claim: I

In combination, a permanent magnet havin the poles thereof turned toward each oles having an air gap therebetween, a rame piece, means for connecting said magnet to said frame low the poles of sai magnet, a support on said portion, bearings on said support, a

pivot bar carried by said bearings, an arma- I iece, said I .frame piece includin a portion disposed beiso- 

